1) Using different MD hardware configurations like "video cards" and "audio cards, will this be a problem for the MD's at boot time (boot from LAN card) for loading the proper video and audio drivers on each device.
Each media director is setup on its own. Meaning, you can configure each and every setting differently for all your MDs. In my test bed, I had an old Fujitsu Siemens Table PC, some old Compaq EVO n400 all working as MDs.
3) I assume a network laser printer is also supported on the DHCP LAN, does anyone have any network scanning ideas/info?
I am not sure I understand what the network printer has to do with an LMCE installation, but basically each MD runs CUPS if I remember right, so they will be able to access whatever network printer is available.
4) As the MD's are essentially a basic computing device, can "open office" run on the MD's as well for desktop computing? I also assume mozilla or kbrowser will work as well.
yes, you have a full KDE desktop at your command.